Overload protective switch



Dec. 12, 1939. w. H. FRANK OVERLOAD PROTECTIVE SWITCH Filed April 22, 1937 Elms-MA L R T E m 8 1N VENTOR.

V ATTORNEY.

Patented Dec. 12, 1939 UNITED STATES PATENT OFFICE OVERLOAD PROTECTIVE SWITCH William H. Frank, Detroit, Mich.

Application April 22, 1937, Serial No. 138,295 15 Claims. (01. 2004s) This application relates to a manual operation switch arranged for operation as an overload protective device whereby it may function as a line control switch, with the control being established 5 manually, or automatically in response to circuit overload.

The switch herein shown is so constructed that it is moved out of on position automatically on prolonged or intense overloads. If the overload i is neither intense nor prolonged, the switch is not opened. If the overload is prolonged but moderate, circuit opening is established through the warping of a bimetal element which moves a contact arm only slightly out of on position;

15 on cooling of the bimetal element thereafter the contact arm returns automatically to on position; the travel of the arm under such circumstances is extremely slight; such movements of the arm are not accompanied by any shifting of go the handle and the switch operates as an automatically resetting switch.

If however, the overload is intense, the arm is caused to move out of on position by combined thermal and electromagnetic force; on such movement of the arm, the handle is shifted and remains out of on position; such handle movement indicates that the arm has been moved out of on position, and that a manual operation is required for restoring the arm to on position.

0 The switch is so constructed that movement of the arm in response to manual movement of the handle takes place with a snap action so desirable in devices of this character.

The switch is so constructed that movement of :35 the arm on the arising of an overload is in no way dependent upon or requires movement of the handle; consequently the device may be considered as trip free, that is to say, manual retention of the handle will in no wayinterfere 40 with automatic movement of the arm out of on position.

The parts are so constructed that after a handle actuation the handle comes to rest in either one of but two positions. This contrasts the pres- 45 ent device from devices heretofore known where more than two rest positions of the handle are necessarily provided. Consequently, when it is desired to move the arm to on position, after its having been moved out of on" position, either 50 by manual operation or by an overload, the handle is moved to its on position in one stroke from its only other off position. In presently known devices movement of the contact arm to of-position is accomplished in either one of 55 two different ways, depending on the position of the handle at that time; and if the handle is in a trip position, movement of the handle to on position is multiple stroke movement, the handle first being moved to a reset position and then moved to on position. 5

The switch is shown as including two different arrangements for causing movement of the contact arm out of on position on overload. One arrangement operates by itself to move the arm but only on prolonged moderate overloads and includes a bimetallic warping element, arranged in circuit with the controlled line and of considerable length, thus having the eifect of increasing the circuit resistance. The other arrangement includes parts which form an electromagnet efiectively operating only on relatively heavy overloads.

The switch hereof is simple of manufacture and operation, and by virtue of its simplicity is extremely economical of space and price.

The switch is so constructed that the travel of the contact arm is generally proportional to the extent of the circuit overload. If the overload be small, the travel is just sufficient to break the circuit but not sufficient to shift the handle. If the overload be intense, the contact arm moves a reat distance, enough to shift the handle.

Inasmuch as contact movement is effected through a bimetal warping element on moderate overloads which is augmented by electromagnetic force on heavy overloads, it will be observed that the speed of movement of the contact is proportional to the extent of the overload. The movement is relatively slow on moderate overloads and rapid on heavy overloads.

For an understanding of the switch reference should be had to the appended drawing disclosing the same. In this drawing,

Fig. 1 shows the switch in on position;

Fig. 2 shows it as if moved manually out of on" position;

Fig. 3 sh ws it as it moved automatically by moderate overload out of on position;

Fig. 4 shows it as if moved automatically on heavy overload out of on position;

Fig. 5 is a fragmentary section view on line 55, of Fig. 1.

Fig. 6 is a view similar to Fig. 5 but showing a modified arrangement of the electromagnetic parts.

The switch includes a sectional casing Ill (shown as if made of one piece) having a slot II in which is disposed and moves a handle I! which is pivotally mounted in the casing on the pivot H. The exposed end of the handle may be ma- 5;

nipulated for manual actuation. Pin I4 pivotally mounts a bell crank type contact arm or lever or bar I6 having on one of its ends a contact I! adapted to make with a stationary contact I8 connected to a binding post I9 for a conductor. On the other end of the lever I6 is a pin 20, and on the handle is a pin 2I, and these are connected by a coiled tension spring 22.

Mounted on a block 23 of the casing is a binding post 24 which is connected by a flexible conductor 25 to a bimetal element 26 which is retroverted as indicated so as to have one part overlie and be electrically connected to and mechanically secured to the lever I6. This same part of the bimetal element is also secured to a small piece of magnetic material, referenced 26. The bimetal element has its other part positioned near a fixed stop pin 29. A U-shaped piece 30 of magnetic material is secured to the casing in position to surround the lever I6 and to have its ends bridged by the other magnet piece 26 to form a magnetic loop around one part of the bimetal element. The controlled circuit is established between line and load conductors through parts 23-24-25-26-I 6-III 8-19.

The operation is as follows: Fig. 1 shows the parts in on position.

For manual operation the handle I2 is rotated on its pivot clockwise to the position of Fig. 2. Spring 22 shifts across the pin I4, whereupon spring 22 causes the lever I6 to rotate counterclockwise about pin I4 to open the circuit. The return of handle I2 from the position of Fig. 2 to that'of Fig. 1 causes the return of the lever I6 to the closed circuit position of Fig. 1, due to the spring 22.

When the lever I6 moves to open circuit position its movement is terminated by the engagement of the part 28 carried thereby with the stationary part 30; its movement to closed circuit position is terminated by the engagement of its contact I! with contact I8.

On the arising and continuing of a moderate overload, the element 26 warps and presses against the stop 29 and moves lever I6 to the open circuit position of Fig. 3, with such movement resisted by spring 22, and with such movement being determined by the degree of warping of element 26, which is only slight, and is not sufflcient to cause the handle I2 to be moved. When the circuit opens under such circumstances, the element 26 immediately cools and returns to its normal position, and during such return the spring 22 causes the lever I6 to follow the element 26 closely and return automatically to its closed circuit position.

The movement of the parts under such circumstances is slight; handle I2 does not move; and the action is an automatic opening and reclosing of the circuit, either cyclically repeated until the overload becomes intense enough to cause the contact to go to the full 01f position (Fig. 4) or discontinued if and when the overload is removed before it reaches the intense stage; and requiring no manual manipulation if the overload does not reach the intense stage; and coming to rest, if the overload does not reach the intense stage, with the circuit closed and with the handle in the on" position, indicating that the circuit is closed. Consequently, unless the overload reaches the intense stage, as far as the attendant is concerned, nothing has happened except a flickering of the circuit and nothing is required of him as to resetting the switch.

However, if the overload is intense to start with, or becomes intense because of prolongation of the moderate overload, the magnetic loop 26-30 will be magnetically energized sufliciently, by the current flowing in element 26, plus the smaller air gap due to movement of the lever I6 under the influence of the thermal element 26, to cause part 26 to be attracted to part 30 and to move quickly to the position of Fig. 4, which is way beyond the other open circuit position, Fig. 3. When the part 28 and with it the element 26 and the arm I6 move to the position of Fig. 4, it moves the lever I6 out of closed circuit position and moves this lever far enough to move the spring across pivot I4 and thus bias the handle I2 out of the on position of Fig. 1

and into the oil position of Fig. 4 where the parts will remain until the handle I2 is returned manually to the position of Fig. 1 thus closing the circuit.

It is to be noted that under the intense overload the combined thermal and magnetic action causes the lever I6 to move rapidly to the of! position. The extent of the overload will determine the speed of movement. For example assume the switch to be a 15 ampere device-a moderate overload would be 200% or 300% of rating or 30 or 45 amperes; the magnetic effect is negligible; and no magnetic eifect is needed, since this current, at low voltages, can be easily ruptured with slow and small amount of break. On a heavy overload or short circuit, however, the current reaches large values of several thousand amperes-say 5000 amperes; the magnetic effect of this current is considerable, and the action of the thermal element 26 is also considerable; the combinedaction results in a quick and considerable movement of the contact I6, as described.

It must also be borne in mind that the current does not immediately build up from 15 amps. to 5000 amps. Because of the electrical inertia (reactance) of the circuit it requires several cycles to reach this value. During this time the thermal element action builds up rapidly and considerably (approximately in proportion to the increase in the square of the current) and as the magnetomotive force increases due to the large current in the bimetal element, the electromagnetic pull increases due to the decreasing of the air gap and causes a quick movement of lever I6.

This movement is further aided by the spring 22 exerting an opening influence on lever I6, after lever I6 is moved to overcenter position by the forces above mentioned. It should be noted that the spring force necessary to be overcome to cause opening of the lever I6 decreases as the movement toward the ofi position increases.

It should also be noted that the proportioning of the parts is such that the forces set up by overload currents (which forces are usually strong but of little amplitude, such as the forces due to warping of the bimetal element) are exerted near the fulcrum of the lever I6 so that little movement of the element 26 will cause an appreciable movement of the contact I! so that as much break as possible will occur between contacts I8.and I! even on slight overloads.

It should also be noted that the amount and speed of contact opening is somewhat proportional to the overload involved. This makes this type of circuit breaker practical as the amount of "break and speed of break of contacts is similarly proportional to the amount of current to be broken and the contact separation necessary to rupture such a current satisfactorily.

Thus, on intense overloads, not only is the contact I! moved very far away from contact l8, but it is caused to remain there until the handle is moved manually; and, on intense overload, .not only does the circuit remain open, but the handle remains in off position, indicating that the circuit is open and that a manual resetting is required.

It will be observed that for reclosing the circuit after an intense overload opening thereof, that but one stroke of the handle is needed, and

that that stroke is the same as the movement through which the handle goes when the circuit is to be closed following any other opening thereof.

It will also be observed that if the magnet produced by parts 28-30 is not of a sufficient number of turns to operate as intended, that it may be desirable to form part 28 as shown in Fig. 6, wherein it is shown as including a multi-turn coil "a connected in circuit with the flexible conductor 25; part 28 will thus form a magnetic coil whose magnetic force will be related to the current flow therein and whose magnetic action will enhance that of the element 26.

Now having described the herein disclosed embodiments of the invention, reference will now be had to the claims which follow which point out the invention.

I claim:

1. In a device of the character described, a movable contact, a handle arranged to move the movable contact with a snap action, and to cooperate with other parts of the device to hold the contact in either one of its controlling positions, a circuit abnormality responsive means arranged to move the contact out of closed circuit position on the arising of a circuit abnormality, the means being arranged to have two different actions, one of which moves the contact a slight distance on moderate abnormality,

and the other of which moves the contact a great distance, but only an intense abnormality.

2. An overload release circuit breaker having an overcenter spring mechanism including two elements, the mechanism being such that when either element is moved overcenter, the other element automatically moves overcenter also, and a circuit current responsive member operatively connected to one of the elements and arranged to move it slightly, on non-prolonged moderate overload, not overcenter but sufllcient to open the circuit momentarily, and thereafter to permit the element to return and the circuit to reclose, the member also being arranged to move the element overcenter'on intense or prolonged overload.

3. An overload release circuit breaker having an overcenter spring mechanism including two elements, the mechanism being such that when either element is moved overcenter, the other element automatically moves overcenter also, and a circuit current responsive member operatively connected to one of the elements and arranged to move it slightly, on non-prolonged moderate overload, not overcenter but suflicient to open the circuit momentarily, and thereafter to permit the element to return and the circuit to reclose, the member also being arranged to move the element overcenter on intense or prolonged overload, the one of the elements moved by the member being a contact arm.

4. An overload release circuit breaker having an overcenter spring mechanism including two elements, the mechanism being such that when either element is moved overcenter, the other element automatically moves overcenter also, and a. circuit current responsive member operatively connected to one of the elements and arranged to move it slightly, on non-prolonged moderate overload, not overcenter but suflicient to open the circuit momentarily, and thereafter to permit the element to return and the circuit to reclose, the member also being arranged to move the element overcenter on intense or prolonged overload, the one of the elementsmoved by the member being a contact arm, the other being an externally exposed handle.

5. In a device of the character described, a movable contact, a handle arranged to move the movable contact with a snap action, and to cooperate with other parts of the device to hold the contact in either one of its controlling positions, a circuit abnormality responsive means arranged to move the contact out of closed circuit position on the arising of a circuit abnormality, the means being arranged to have two different actions, one of which moves the contact a slight distance on moderate abnormality, and the other of which moves the contact a great distance, but only on intense abnormality, the first mentioned movement of the contact not being accompanied by shifting of the handle, and being followed automatically by return of the contact to its original position.

6. In a device of the character described, a movable contact, a handle arranged to move the movable contact with a snap action, and to cooperate with other parts of the device to hold the contact in either one of its controlling positions, a circuit abnormality responsive means arranged to move the contact out of closed circuit position on the arising of a circuit abnormality, the means being arranged to have two different actions, one of which moves the contact a slight distance on moderate abnormality, and the other of which moves the contact a great distance, but.

only on intense abnormality, the second mentioned movement of the contact causing shifting of the handle and being not followed by return of the contact except if the handle be returned. '7. In a device of the character described, a movable contact, a handle arranged to move the movable contact with a snap action, and to cooperate with other parts of the device to hold the contact in either one of its controlling positions, a circuit abnormality responsive means arranged to move the contact out of closed circuit position on the arising of a circuit abnormality, the means being arranged to have two different actions, one of which moves the contact a slight distance on moderate abnormality, and the other of which moves the contact a great distance, but only on intense abnormality, the first mentioned movement of the contact not being accompanied by shifting of the handle, and being followed automatically by return of the contact to .its original position, the second mentioned movement of the contact causing shifting of the handle and being not followed by return of the contact except if the handle be returned.

8. In a device. of the character described, a movable contact, a handle arranged to move the movable contact with a snap action, and to cooperate with other parts of the device to hold the contact in either one of its controlling positions, a circuit abnormality responsive means arranged to move the contact out of closed circuit position on the arising of a circuit aboperate with other parts of the device to hold the contact in either one of its controlling positions, a circuit abnormality responsive means arranged to move the contact out of closed circuit position on the arising of a circuit abnormality, the means including two separate parts, one of which responds to abnormality of any degree, and the other of which responds only to intense abnormality, the first one being arranged to operate by itself, on a moderate abnormality, to move the contact a slight distance, and the other, when energized by an intense abnormality, causing the contact to be moved a great distance, the first mentioned part comprising a bimetallic current responsive warping element and the second mentioned means comprising an electromagnet.

10. A manually operable snap switch, means for automatically opening the switch on moderate overloads of the circuit controlled by the switch and for automatically closing the switch thereafter, the means operating cyclically for opening and closing the switch unless the overload becomes intensely abnormal in the meantime or unless the switch is opened manually, or unless the overload is removed, and means for automatically opening the switch on intense overload and arranged to hold the switch open after such an opening movement thereof.

11. A manually operable snap switch, means for automatically opening the switch on moderate overloads of the circuit controlled by the switch and for automatically closing the switch thereafter, the means operating cyclically for opening and closing the switch unless the overload becomes intensely abnormal in the meantime or unless the switch is opened manually, or unless the overload is removed, and means for automatically opening the switch on intense overload and arranged to hold the switch open after such an opening movement thereof, and to move the switch handle to open position.

12. A manually operable snap switch, means for automatically opening the switch on moderate overloads of the circuit controlled by the switch without moving the handle to open position and for automatically closing the switch thereafter, the means operating cyclically for opening and closing the switch unless the overload becomes intensely abnormal in the meantime or unless the switch is opened manually, or unless the overload is removed, and means for automatically opening the switch on intense overload and arranged to hold the switch open after such on opening movement thereof.

13. A manually operable snap switch, means for automatically opening the switch on moderate overloads of the circuit controlled by the switch without moving the handle to open position and for automatically closing the switch thereafter, the means operating cyclically for opening and closing the switch unless the overload becomes intensely abnormal in the meantime or unless the switch is opened manually, or unless the overload is removed, and means for automatically opening the switch on intense overload and arranged to hold the switch open after such an opening movement thereof, and to move the switch handle to open position.

14. A manually operable snap switch, means for automatically opening the switch on moderate overloads of the circuit controlled by the switch and for automatically closing the switch thereafter, the means operating cyclically for opening and closing the switch unless the overload becomes intensely abnormal in the meantime or unless the switch is opened manually, or unless the overload is removed, and means for automatically opening the switch on intense overload and arranged to hold the switch open after such an opening movement thereof, and to move the switch handle to open position, the switch being closable thereafter by movement of the handle to closed position.

15. A manually operable snap switch, means for automatically opening the switch on moderate overloads of the circuit controlled by the switch without moving the handle to open position and for automatically closing the switch thereafter, the means operating cyclically for opening and closing the switch unless the overload becomes intensely abnormalin the meantime or unless the switch is opened manually, or unless the overload is removed, and means for automatically opening the switch on intense overload and arranged to hold the switch open after such an opening movement thereof, and to move the switch handle to open position, the switch being closable thereafter by movement of the handle to closed position.

WILLIAM H. FRANK. 

